I've had some trouble with my '99 Ranger 4x4 with 5-spd manual and 4.0L V6. First, it would not want to start. Changing gas seemed to help, from Diamond Shamrock to Chevron. This came and went. I've experienced some rough idling from time to time, but never predictable or constant. It is slow to return to idle, also, though not all the time, often hanging at about 1,200 rpm before finally dropping down to 800 or so. Now I get a "Check Engine" light. So far this has happened three times, and it won't go away until I have the dealer check the code and reset it. All three times it's occurred, I've been driving at a steady speed of about 45-50mph. The diagnostic every time has been a "lean code" (I haven't seen it, and am unfamiliar with Fords OBD codes.)
I recently replaced the oxygen sensors, and while this seemed to improve the way the truck ran (start-up, throttle response), it didn't prevent the third incident of "Check Engine" light.
It's in the shop now, and the mechanic says he's checked everything and he thinks it's the fuel pump. My cost to replace the pump is over $400.
So, hive mind, any thoughts?